Oxidation of the separator, e.g., separators for lead/acid batteries, reduces a battery's cycle life, and thereby reduces the effective life of the battery. Oxidation causes the embrittlement (measured by, for example, loss of % elongation) of the separator which leads to partial or complete failure of the battery.
Contaminants typically originate from the water and/or the sulfuric acid added to a battery, as well as from impurities in the alloys and active materials that comprise the electrode plates, may cause oxidation. Such contaminants typically include the transition metals of the periodic table, for example: chromium (Cr), manganese (Mn), titanium (Ti), copper (Cu), and the like. Contaminant levels (e.g., Cr, Mn, and/or Ti) of greater than about 2.0 ppm [2.0 mg/L] are not recommended. Cu contaminants greater than 26 ppm [26 mg/L] are not recommended. In batteries without contaminants (e.g., Cr), the separator may have a life of about 7 years, but with contaminants (e.g., 5 ppm Cr), the separator deteriorates in about 6 months.
In some areas of the world, for example, Asia, lead/acid batteries are sold as ‘dry charge’ batteries. These dry charge batteries are purchased without the water/acid included. The dry charge battery has a longer shelf life. However, the user may not be careful to fill the battery with uncontaminated water/acid. The contaminated water/acid will lead to oxidation of the separator and ultimately to battery failure. The contaminants in the water/acid may be sourced from the water/acid containers, e.g., steel drums.
U.S. Pat. No. 5,221,587 discloses the use of latex in the separator to prevent antimony (Sb) poisoning of the lead/acid battery. Antimony poisoning does not cause separator oxidation; instead, antimony poisoning causes water loss from the electrolyte. Antimony is sourced from the lead plates (electrodes) of the battery. Antimony is used as an alloying agent in the lead to improve the manufacture of the plates and the cycle life of the battery. Those of ordinary skill would not consider the teachings of U.S. Pat. No. 5,221,587 in arriving at a solution to the separator oxidation problem mentioned above.
U.S. Pat. No. 6,242,127 discloses the use of cured, porous rubber in a conventional polyolefin separator to improve the electrochemical properties (antimony suppression) of the separator.